1. Field of the Invention
The field of the invention relates to microelectromechanical systems (MEMS) and organic light-emitting diode (OLED) devices, and more particularly, to methods and systems for packaging MEMS and OLED devices.
2. Description of Related Technology
Microelectromechanical systems (MEMS) include micro mechanical elements, actuators, and electronics. Micromechanical elements may be created using deposition, etching, and or other micromachining processes that etch away parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. One type of MEMS device is called an interferometric modulator. As used herein, the term interferometric modulator or interferometric light modulator refers to a device that selectively absorbs and/or reflects light using the principles of optical interference. In certain embodiments, an interferometric modulator may comprise a pair of conductive plates, one or both of which may be transparent and/or reflective in whole or part and capable of relative motion upon application of an appropriate electrical signal. In a particular embodiment, one plate may comprise a stationary layer deposited on a substrate and the other plate may comprise a metallic membrane separated from the stationary layer by an air gap. As described herein in more detail, the position of one plate in relation to another can change the optical interference of light incident on the interferometric modulator. Such devices have a wide range of applications, and it would be beneficial in the art to utilize and/or modify the characteristics of these types of devices so that their features can be exploited in improving existing products and creating new products that have not yet been developed.
Desiccants are commonly used in MEMS and OLED devices to keep the internal environment of the display device dry during the device's operational lifetime. The desiccant may be in different forms, shapes, and sizes. For example, materials like CaO and zeolites may be used in the form of a thin patch or a thin hardened paste to absorb moisture inside the device package. The materials can be attached to a surface in the display device, such as a backplate, with pressure sensitive adhesive, for example. Patches and pastes are applied with a typical thickness of 80-200 microns. These patches and pastes therefore constrain the minimum thickness of the device, because sufficient room must be provided for both the desiccant and movable element(s) inside the display device package. To make room for patch or paste desiccants without substantially increasing the thickness of the display package, additional manufacturing steps may be employed. A cavity may be chemically etched into a display substrate, for example, so that desiccant can be deposited in the manufactured cavity.
The effectiveness of patch and paste desiccants is also limited because such desiccants are delivered with a binder in the form of a matrix, whereby, for example, a Teflon binder includes 15 to 20% embedded desiccant. Using a binder or solvent to apply a desiccant to a surface is not optimal in the presence of sensitive MEMS components, however, as the binder or solvent can release contaminants into the display package as it evaporates. Use of solution processing to apply a desiccant also results in outgassing of contaminant gasses inside the display package.
The efficacy of patch and paste desiccants is further limited because they are not applied uniformly across an entire surface in the display device package. They are typically attached such that they cover one region of a surface in the display device, leaving other regions uncovered. The presence of the desiccant on some areas and not others, and the proximity of the desiccant to sensitive interferometric modulator components, can impair the electromechanical behavior of the modulator and degrade device performance.
The continued reduction in display device dimensions restricts available methods to manage the environment within the display device package because there is less area to place a desiccant within the package structure. Although the area of a packaging structure susceptible to influx of water vapor may remain the same or be slightly reduced as package structures are reduced in size, the area available for a desiccant is reduced dramatically in comparison.